The present invention relates to a hydrogen combustion heater for heating a fluid (e.g., water) by a heat generated by a catalytic oxidation of hydrogen gas.
There are various combustion heaters in which a fluid is heated through a heat exchanger by a heat generated by a catalytic oxidation of a fuel gas. It is preferable to use a hydrogen combustion heater, for example, for heating of interior of an electric vehicle equipped with a hydrogen fuel cell, since a single fuel source (i.e., hydrogen gas) can be used for both of the heater and the fuel cell.
A hydrogen combustion heater is operated by bringing a mixture of hydrogen gas and air into contact with a catalyst to achieve a catalytic oxidation of hydrogen gas. It is necessary to get a suitable temperature for achieving the catalytic oxidation. Upon starting the operation of a hydrogen combustion heater, it is known to conduct a spark ignition of a mixture of hydrogen gas and air at a position upstream of the catalyst in the heater, thereby achieving a high temperature and the subsequent combustion of the hydrogen gas. Thus, it becomes possible to heat the catalyst to a temperature suitable for the catalytic oxidation by passing the resulting combustion gas of high temperature through the catalyst.
The above-mentioned spark ignition, however, can be achieved, if the mixing ratio of hydrogen and air is a value causing explosion or deflagration. Besides such explosion problem, the combustion temperature caused by the spark ignition may become too high. This may cause a high thermal stress on a heat exchanger of the heater due to a large temperature difference between the heat exchanger and its fluid. Furthermore, the formation of nitrogen oxides may become too much.
Japanese Patent Unexamined Publication JP-A-2000-291917 discloses a hydrogen combustion device. This device includes a separate heater for preheating a catalyst used in a catalytic oxidation of hydrogen gas.